JPH0125442B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an integrated circuit suitable for integrating filters, equalizers, etc. used in electronic circuits.

[Prior art]

Conventionally, in electronic circuits, in order to obtain the desired signal,
Low-pass, high-pass, and bandpass filters (hereinafter referred to as LPF)
HPF, BPF) and a phase equalizer are used.
However, these are difficult to integrate for the following reasons, so they are generally referred to as integrated circuits (hereinafter abbreviated as IC).
It consists of external resistors, capacitors, and inductances, which increases the number of components.
For this reason, these filters are used in small electronic circuits and
This was a major factor hindering efforts to reduce weight and cost. Particularly in portable equipment where mobility is important, miniaturization and weight reduction are important basic performances, and up until now it has been difficult to integrate the above filters into ICs. Below, we will explain the disadvantages of integrating filters and equalizers with simple configurations.

First, in ICs, even if they are formed on the same chip, the absolute value accuracy of integrated elements is poor (usually ±20 to 30
%), it is difficult to obtain highly accurate filter or equalizer characteristics using integrated resistors and integrated capacitors. For example, if we try to integrate a bandpass filter consisting of resistors 1 and 2 and capacitors 3 and 4 as shown in Figure 1, this
The low and high frequency shearing frequencies cl and ch of the BPF are cl=1/2πR ₁ C ₃ , ch=1/2πR ₂ C ₄ (R (code number) and C (code number) are each resistance , indicates the value of capacitance (the same applies hereafter), and if we assume that the variation in resistance and capacitance within the IC is ±30%, the cut-off frequency will vary significantly from -40 to +200%. . Note that 5 to 7 are buffer amplifiers that can be easily integrated, and 8 and 9 are input and output terminals of the BPF. Moreover, integrated resistors are usually
It has a temperature characteristic of around 2000PPM/℃.For example, in the case of Figure 1, if the temperature changes by ±50℃,
The disadvantage is that cl and ch increase or decrease by ±10%.

Second, once integrated, it is difficult to finely adjust the filter characteristics, reducing the degree of freedom in designing the electronic circuit.

[Purpose of the invention]

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to provide an integrated circuit in which filters and equalizers can be integrated with a simple configuration and high-precision characteristics, and the electronic circuit can be made smaller and lighter. be.

[Summary of the invention]

In order to achieve the above object, the present invention configures a filter or equalizer circuit with a variable resistance element consisting of an integrated resistor, an integrated capacitor, and an integrated transistor, and uses the value of the variable resistance element as a control signal. Twist it so that it can be adjusted.
Further, the value of the variable resistance element is changed depending on the temperature, thereby eliminating or reducing the temperature characteristic of the characteristic of the filter or equalizer circuit.

[Embodiments of the invention]

The present invention will be explained below using examples. FIG. 2 shows an embodiment of the present invention, and FIG. 3 is a diagram explaining the operation of the embodiment of FIG. In Figure 2, 1
0 to 12 are NPN transistors, 13 and 14 are
PNP transistors, 15 to 17 are NPN diodes, 18 to 26 are integrated resistors, 27 is an external variable resistor, 28 is a fixed current source, 29 is a dotted line indicating the IC integration range, 30 to 34 are IC external terminals, 35 ,36
are constant current sources each composed of a resistor and a transistor, and 37 is a current control circuit that changes the constant current amount of the constant current sources 35 and 36 according to the signal from the CI external terminal 33, and is the same as in FIG. Alternatively, equivalent parts are denoted by the same reference numerals. Further, the IC external terminal 31 is a power supply voltage terminal of the IC.

A signal input from the IC external terminal 30 is supplied to the base of the transistor 10 via the buffer amplifier 5. The emitter of the transistor 10 is
Constant current source 3 consisting of transistor 11 and resistor 20
5, and the amount of current of the constant current source 35 is
I ₁ is changed via the current control circuit 37 according to the voltage generated at the IC external terminal 33. Further, the signal generated at the emitter of the transistor 10 is transmitted to the resistor 18.
and is input to the buffer amplifier 6 via the capacitor 3. Next, the output of the buffer amplifier 6 is inputted to the buffer amplifier 7 via the capacitor 4, and outputted to the outside of the IC via the buffer amplifier 7. Note that at the input terminal of the buffer amplifier 7,
A series circuit of a resistor 19 and a diode 17, and a constant current source 36 consisting of a transistor 12 and a resistor 21 are connected. Also, the amount of current of the constant current source 36
I ₂ is changed in accordance with the voltage signal generated at the IC external terminal 33, as in the case of the constant current source 35 described above. By the way, the current control circuit 37 is a circuit based on a differential amplifier consisting of a pair of PNP transistors 13 and 14, and the collector of the PNP transistor 13 is controlled according to the voltage of the IC external terminal 33 determined by the external variable resistor 27. This circuit changes the voltage at the connection point between the constant current sources 35 and the anode of the diode 16, that is, the input voltage of the constant current sources 35 and 36, and changes the current amounts I ₁ and I ₂ of the constant current sources 35 and 36.

By the way, what about transistors or diodes?
The resistance γ _e of the PN junction with respect to minute amplitude is expressed by γ _e =kT/qI (k: Boltzmann constant, T: absolute temperature, q: amount of electron charge, I: amount of current flowing through the PN junction). Therefore transistor 1
0 and the diode 17 as γ _e10 and γ _e17 , respectively, γ _e10 = kT/qI ₁ and γ _e17 = kT/qI ₂ . Therefore, the circuit shown in FIG. 2 is represented by an equivalent circuit as shown in FIG.
The HPF is configured in the latter stage. In Figure 3,
38 indicates γ _e10 and 39 indicates γ _e17 . At this time, the cutoff frequencies cl and ch of the LPF and HPF, respectively, are expressed as cl=1/2π(γ _e10 +R ₁₈ )C ₃ and ch=1/2π(γ _e17 +R ₁₉ )C ₄ . Therefore, γ _e10 and γ _e17 are the current amounts I ₁ and I ₂ that change according to the voltage signal of the IC external terminal 33.
Therefore, γ _e10 and γ _e17 are external variable resistors 2
7, integrated elements 3, 4, 18,
Therefore, it is possible to realize a filter that absorbs 19 variations and has a desired cutoff frequency.

Furthermore, since the relative value accuracy of integrated resistors or integrated capacitors within the same IC chip is extremely good,
Variations in integrated resistors 18 and 19, integrated capacitance 3
The variations in and 4 are very consistent. Therefore, if γ _e10 is changed by adjusting the voltage at the IC external terminal 33 to absorb the variations in R ₁₈ and C ₃ , the change in γ _e17 will be the same as in R ₁₉ and C ₄ . Since it acts to absorb variations, desired BPF characteristics can be achieved by adjusting one IC external terminal signal.

Of course, one adjustment IC for each LPF and HPF.
By providing external terminals, each cutoff frequency can be adjusted accurately and highly accurate BPF characteristics can be obtained.

Also, as mentioned in the conventional example, the value of the integrated resistor is
It has a temperature characteristic of approximately 2000PPM/℃.
In contrast, in the present invention, the current control circuit is provided with temperature characteristics that reduce fluctuations in the cut-off frequency due to the temperature characteristics of the integrated resistors 18 and 19, thereby reducing temperature characteristics fluctuations. Realizes fewer filter circuits. This point will be explained below.

Since the voltage V ₁₄ generated at the IC external terminal 33 is determined by the division ratio of the variable resistor 27, it has no temperature characteristics. On the other hand, the base voltage V ₁₃ of the transistor 13 has a temperature characteristic due to the temperature characteristic of the base-emitter voltage V _BE of the diode 15 (usually -2 mV/° C.). If the temperature increases now, the voltage V ₁₃ will decrease, the current flowing through the resistor 24 will increase, and the collector voltage of the transistor 13 will increase. Therefore, constant current source 35,
The current amounts I ₁ and I ₂ of 36 become large, and γ _e10 and γ _e17 become small. That is, as the temperature increases, the integrated resistor 1
The values of 8 and 19 become large, but γ _e10 and γ _e17 become small, and γ _e10 +R ₁₈ , γ _e17 which determines the shearing frequency
+ _R19 temperature change will be reduced.

In other words, in contrast to the temperature characteristics of the integrated resistor that determine the characteristics of the filter, the present invention provides the current control circuit with temperature characteristics that reduce fluctuations in the cutting frequency due to the temperature characteristics of the integrated resistor. A filter circuit with less variation in temperature characteristics can be realized.

Of course, if not only the integrated resistor but also the integrated capacitor, for example, has temperature characteristics, it is obvious that the influence of this can be reduced.

Furthermore, portable VTRs and the like are required to be smaller and lighter in order to improve usability. Therefore, by forming and integrating the resistor as a thick film resistor on a ceramic substrate, and by applying a laser to the thick film resistor and increasing the resistance value by damaging the thick film resistor, the resistance value can be adjusted quickly and easily. Automatic laser trimming technology is widely used as an essential technology.

According to the present invention, when adjusting the filter characteristics using the above laser trimming technique, the variable resistor 2
By trimming and adjusting the resistance values Ra and Rb on the power supply voltage side and the ground side (resistance value increases), terminal 3
Since the voltage of No. 3 can be increased or decreased, the resistors Ra and Rb can be set to optimal values from the beginning, which has the advantage that the adjustment time can be shortened.

In the embodiment shown in FIG. 2, the current control circuit has a temperature characteristic to compensate for the temperature characteristic of the filter characteristic, but the same effect can be achieved even if the signal applied to the IC external terminal 33 has a temperature characteristic. It is clear that the effect is obtained.

〔Effect of the invention〕

As described above, according to the present invention, there is an effect that integration of filters and equalizer circuits can be realized with high accuracy using a simple circuit configuration. This greatly contributes to the miniaturization and weight reduction of electronic circuits, which in turn can contribute to the miniaturization and weight reduction of VTRs and other devices that use such electronic circuits.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional filter circuit, FIG. 2 is a circuit diagram showing an embodiment of the filter integrated circuit of the present invention, and FIG. 3 is a diagram explaining the operation of FIG. 2. 5 to 7...Buffer amplifier, 8...Filter input terminal, 9...Filter output terminal, 3, 4...Capacitance, 3
5, 36...constant current source, 29...range of integrated circuit, 3
7...Current control circuit, 27...External variable resistor.

Claims (1)

[Claims] 1. In an integrated circuit in which multiple filters consisting of integrated capacitors and integrated resistors are integrated, multiple variable resistance elements are connected to each of the multiple integrated resistors and whose resistance value changes depending on the flowing current, and a transistor is connected to each of the multiple integrated resistors. Contains multiple variable current source circuits that supply current to the variable resistance element, and controls the amount of current flowing to the variable current source circuit to change the current flowing to the variable resistance element and adjust variations in the cutoff frequency of the filter. and a current control circuit having a diode-connected transistor that changes the current flowing through the variable resistance element with changes in ambient temperature to compensate for the temperature characteristics of the integrated resistor. .